Dee. 1941 358 HOPKINS-"PIGMENT PADDING PROCESSES O F APPLYING VAT DYES"

Jery good,

rven with blur vat dyes

irrv good; the lonuer the re- durtion rncreq, the betrer thr fHRtnCS8

rEprciU~lY 111 llght Shadrs

v'ery good to rxcellrnt

'adding niny be coiltinunus. hiit reduction and

lng are not rontinuons

further pl'Wl'HE-

Tho Lecturer replied that the vat, and azoic dyes for cellnlose acotato were of high fastness and gave dyeings of satisfactory faatness to milling.

Ur. T. A. Foster, referring to considerablo modern activit.y in dyeing "in tho niass' by incorporating dyes or lakes in tho spinning solution, askocl whether i t was posnible to produce khaki shadus on CelanoRe by such mothods.

Tho Lecturrr rcplicd that, pract.ically any shade could be produced, hut further part.irnlars could not be given on t,hat occasion.

Mr. J. B. Simpson askotl whethor any methods were available for cloaring Fibro from stains produced when dyeing srnall quarititios of colluloso acetato fibre also prosont in the matorial.

Moderatr

I'nor, but Improved by furthiv redurtion on thr Jir

Modrrnte

Contlnuouf

The Lecturer stated t,hat usual stripping treatments were with t,he familiar hypochlorites for oxidation, or hydrosulphites for reduction. Active charcoal, con- veniently in a soap bath, provided an alternative.

In reply to a furthor question as t,o whether it was possible to apply anthraquinonoid and allied vat dyes to Celanose by using an alkali carbonate instead of the usual caustic alkali, the Lecturer said that tho type or strength of alkali (in the absence of saponificat,ion of tho fibre)did not play a significant part in tho vat dyoing of cellulose acetate. The dyeing or non-dyeing property was specific to the individual dye. Those vat dyes which tlyo colluloso acet.ate are predominantly of the intligoitl class. Tho fact that these dyes are generally applied from baths of relatively low alkalinity was beside the point as it was tho intrinsic property of each dye which mattered, not the alkalinity of the dyebath.

SCOTTISH SECTION

Pigment Padding Processes of Applying Vat Dyes Mooting held a t St. Enoch Hotel, Glasgow, on 1st November, 1940, Mr. J. Mum, jwir., in the chair.

W. E. H ~ P K I N S

Every tlytrr who is familiar with tho 1180 of vat dyes has difficwlty, at. some time or other, in obtaining good prnet.ration,whethPron yarn or piece. In the last few years, exacting conditions in the trntlo have compelled dyers to pay part.icnlar att,ontion to this problem as the trade, in gnneral, has been much more critical as regards results.

In viow of this position, therefore, considerable interest hris boon takon i n tho pigment padding process of applying vat dyes, since iL is rnoro efficient, consistent and reliable than other modified vat dyeing processes, and, in its various forms, it han now been adopted by the trade for oert>ain specific purposes.

The pigment padding process was originally introducod as a moans of obtaining well-penetrated shades on tightly woven materinls, 0.g. cotton drills, duck cloths, and linen furnishings and tlrostl goods, and yielded results which woro far in atlvtmco of ordinary jig-dyed styles. However, after prtwtical oxporience of the process had boon gained ant1 irnprovcrnonts made in padding oils and in tho ordinary physical contlit.ion of vat dyes, it was realiseti t,hnt i t offorod othor advantages, and for this reason it is used n o w fur producing levol palo shades on pieco goods, including cotton-viscose rayon union piece goods, in all dcpths of Hhade, looso cotton and looso viscose rayon fibre, t.wistctd viscose rayon yarns in pale shades and mercerised cottons in light shades dyed eit,her in hank or circulating machines.

The following Tables show the advantages and dis- advantages of the pigniont, padding process compared with other woll-known methods of dyeing pioce goods, yarn and loose materials.

From the comparative results given in Tables I and 11, it is obvions that t.he pigmenting process can advan- tagcoi~sly 110 omployotl in special cams for almost any typo of vat dyeing and, theroforo, it is recornmontled that dyers should consitlor tho adoption of this process in oases whore clifficiilty is being oxporiencod in obtaining satisfactory results by normal dyeing processes, i.e. if the results given in tho Tahlos show that an atlvantago is to be gained by pigmenting.

Tho pigmenting procoss of applying vat dyes to cellulosic fitbrics consists essentially of applying the dispersed and unrediiretl dye to tho dry material anti roducing the dyo i j 7 , n i t u with emistic socln and sodium hytlroeulphite, then oxitlising, washirig and soaping. Matter8 that. need careful attention if the most satisfactory results aro to be obtained, a r e

(1) Satisfactory protreatment and drying of the materials; (2) correct choice of padding oil; (3) careful selection of dyes; and (4) padding mangle.

P.reparation of Piece (r'ootde-The preparation of a itniformly absorbent material is of groat importance, since faults which only show up after tlyoing may be directly attributed to a faulty prepare. In general, light goods, e.g. poplins, shoetings, etc., should be prepared in rope

form, whereas hoavior goods should always bo processed in open width. The processos of proparation are quito normal and a re -

(2) Washing and kior-boiling. (3) Washing. bleaching, scouring and washing. (4 ) Drying and merrerising. (5) Washing thoroughly and drying to even width.

( I ) Singeing and desizing.

TABLB I CO1IPARIBON OF THE ILESULTS OBTAINED I N ])VEIN0 PIEOR GOODY

1.cvelness ..

Washinu fnstnesa

Penctratlon

rrodllction

Advantftyrs and tlinad

vantages

___. .

L11 Depths Only liuht availablct shades

pract~icable

"roduct ion In fairly rapid and consistency of results IR oh- talnrd. Shade matching IS fairly simplc and all types of slindrs are readily ohtaliid w1t.h u grentrr choice of sult- able dyes. FaRtnrss Is q11it.e satiafnc- tory 88 well ns

and penetration of shades. Better tone

the ICVehiCRS

Ylrlda onli mcdincrr r tmlh. YlItiSfaC- tory fQ pale shades only. Llmlta- tlon of sntisfac- tory dvrs TlitRrult to work with rom bination8 Washing fHstueas 0 an inferio order

rrsults on cot tan-vi S C O L I ~ rayon piece goods

Rdativt~ly oor, Imr F icularly

in light

Rxrrllent

rhades

Unaatis- factory

Not ron- tlnuoua

:onsistr nry

isnotgood penetrii- tion is poor an( levrinrss is poor i i pale shndcs with lIuIllY dyt.

Of reE1lltE

Dyeinp or Padding

with Soletloll

INrs

Only llght shades

availablp

Excellelit

Modrrnte; lniproved by r1YIuc- tinn, oxl- dation, etc., ns in vat dyeing

Excellent

Paddilra incthoil in cont>illu- o w

Only satin- fnctnry for pale shades, but iesults nre excellciit

Dee. l o l l HOPKINS-“PIUMENT PADDING PROCESSES OF APPLYING VAT DYES” 359

TABLE I1 COMPARISON OF RESULTS OBTAINED IN DYEING (A) LOOSE COTTON

AND VIRCOsE FIBRO‘ (B) MERCERISED COTTON AND VISCOSE RAYON YARNS; AND’(C) YARNS’ ON CHEESES, BOBBINS, COPS, C0118. AND B ~ A X WARPS.

(A) and (B) I n oprn veenei -~

In circuiatine mnchineu

(C)

Tn open or closed cir- minting niachines

__ _ _

Mgmenting PIOWRE

Pigmenting occura evenly throughout the dry ninss on wetting out and there- fore level shades are ob- tained. No rvtartllng agents nre required. Excrlient penetration

Sperialiy r rcommend~d for pale shadcu. Plgnirnting IS even without flltratlon and since reduction takes pince in eilu, lnvcl shndcs arr obtained. Particularlv snit- able for pale shades, yellow- green and blue-vloiet rnix- tures

Specinlly recommended for dyeing pale shaden, pnr- ticulnrly mixturns. Lrvpl nud wrll penetrnted dye- ings obtained without wing retartling ngents

Dyeing Procesa Unievcl shndes. Re-

tarding went8 re- quired with many dyes. Penetration of nn inferior order

Difflculty In obtain- ing level pnle shades with many dgestiitfs for which retarding agents are reqiiirrd

Level pale ~hadcs obtained with diffl cuity, especially i n mixtures. for rvhirh retrtrtling ngnnta nre nerpssnry

Mercerking may be carried out before bleaching or, in some cases, after dyeing. It is not always necessary to bleach the goods, e.g. when t,hey have to he dyed in deep shades. The goods should he evenly dried prior to padding, otherwise the absorbency of the material for the padding liquor will vary with the moisture content of the cloth and result in uneven padding.

Heavy cotton drills and uniform rloths are usually dyed in the grey &ate and should be particularly well singed. Also, these goods, in open width, should be thoroughly boiled with caustic soda prior to padding, in order to remove “motes” which may give a speckled appearance to the resultant dyeings, especially with light shades.

Linen piece goods should not be processed in rope form prior to padding, and care should he taken to ensure that the surface of the cloth is not injured mechanically. Linen goods are often causticised prior to dyeing by treating t,hem in open width with caustic alkali and allowing t,hem t,o lie before being washrtl, scoured and framed or stent,ered to regular width.

Loose Colton, Viacose Rayon and Cotton Yarns-Loose cotton is usually boiled in alkali, bleached and dried prior to padding. It need only be bleached when light and bright shades are required. Viscose rayon goods are scoured in hot soap and ammonia or hot soap and soda solutions prior to washing and drying. Bleaching is not. necessary since this is usually rarried out after the desulphurising treatment during manufacture.

Cotton yarns are also kier-boiled and bleached, if necessary, prior to waahing and drying. If the pigmenting process is t,o he carried out in pressure machines, pretreat- ment of the yarn may also he carried out in these machines.

Padding OidMurh of tho success of the pigment padding process depends on the use of a suitable padding oil and considerable study has been given to t.his problem with the result t,hat Calsolene Oil HS has been found to comply with all the required properties and is, therefore, specially recommended for pigment padding. This product has been in universal use for a considerable period end yields excellent results. Padding oils should possess the following properties-

(1) High efficiency in wet,ting out fibres over a wide range of temperatures; (2) freedom from “cracking” during padding and from any tendency to cause aggrega- tion of the minute dye part,icles; (3) ability to hold the dye particles in perfect suspension for long periods; (4) stability to acids and alkalis; and (5) comparative freedom from frothing during padding.

Calsolene Oil HS satisfies all the above requirements and, in addition, has a slight retarding action on the dyeing properties of vat. rolours, thus promoting additional levelling during reduction. In tho pigment padding of piece goods, 1% Calsolene Oil HS should he used on the volume of the padding bath, i.0. 1 Ib. per 10 gall., but in

the pigmenting of loose fibres and yarns, much lower concentrations may be used.

Dyea-Successful padding can only he achieved by using vat dyes in such a physical stat,e that they form highly dispersed suspensions in the weak padding oil liquor, and must not settle out or form aggregates under wide variations of temperature. Caledon vat dyes, therefore, are specially prepared for this process; they are marketed as Paste Fine, Grains, or Powder Fine.

The Paste Fine brands in various concentrations satisfy demands when the dyes are in regular use and are not left standing in open drums for long periods. Should it.‘be necessary to leave partially filled drums standing, they should be covered with a wet cloth before the lids are put on in order to prevent local drying of the Paste on the sides of the drum aa this would tend to form hard lumps which would cause specky pads. Should these conditions arise, suspensions of paate should always bewell sieved prior to use in the padding mangle. It. is advisable to add the Calsolene Oil HS to the diluted dye when preparing the padding liquor because, under certain conditions, aggregation of the dye may occur if the oil is added to the concentrated dye prior to dilution.

The Caledon Grain t,ypes are part,icnlarly recommended for the pigment padding process, since they yield extremely fine and stable suspensions when diluted with either hot or cold water, these suspensions being so fine that the dye particles will pass through filter paper. The grains also have the advantage of being non-dust,ing and, as they are very bulky, are easily and accurately weighed. The Caledon 300 Powder Fine types also yield very satisfactory results, hut as they are in a relatively high concentration, greater care should be taken in weighing and completely wetting out prior to dilution.

The preparation of Caledon dyes in Pmte, Grain and Powder Fine forms siiit,able for pigment. padding, has received much attent.ion in rcccnt years from the physical point. of view, but, even yet there arise, from time to time, problems which have not yet been sat>isfactorily explained, e.g. some dyes are far more amenable to treat,ment, than others, although similarly constitut,ed, and require a good deal more processing to prepare in a “fine” form. Again, in certain cases, it is possible to carry out paddings under ident,ical conditions with similar dyes which differ slightly in physical condition, although both are satisfactory, with the result that, after reduction and dyeing, one padding is weaker than the other, although theoretically there is the same amount of dye present in each case and there is no apparent difference in the result,ant degree of ponetration. I t might be concluded that the difference in particle size of the dyes could cause the difference, but particle size only concerns variation in pigment covering value and penetrat,ion and, therefore, there may possibly be some variation caused by slight difference in reduction after padding.

From a manufacturing point of view, Powders Fine and Grains are more difficult to prepare than Pastes Fine, and the higher the concentration the greater the difficulty, so that a special technique has to be adopted in preparing such brands. Furthermore, the preparat,ion of dry brands is becoming of increasing importance, since, in this country, such types are now preferred to pastes for obvious reasons and, moreover, there is no satisfactory method of exporting paste brands, especially to tropical countries, wit,hout causing a certain amount of drying.

Summarising, therefore, it is the present author’s experience t,hat the ideal type of vat dye for pigmenting, whether in paste or dry form, should bo capable of readily forming a uniform suspension of discrete fine particles, and that the actual form of particles, provided they are sufficiently fine, is of secondary importance, although there are perhaps several exceptions to this rule.

Padding Mangle-Various efficient types of padding mangle8 are available; they give a soft, flexible nip on the clotah hy expression between hard and soft rubber rollers. The most popular types aro vertical mangles provided with 2 or 3 rollers and giving 1 or 2 immersions, respect,ively. in the padding liquor, hut it, is an advantage to give as many immersions in tho liquor as possible t,o ensure thorongh penetration of the goods in the minimum of time; with this object in view, various somewhat complicated types of mangles have been introduced by

360 HOPKINS-"PIGMENr P.4DUINC: PROCESSES O F APPLYINC: VAT DYES" DW. 1941

<'ontinentaI nianufncturera. tlweacling thew niangks are show'n in Fig. 1.

The designs antl nietliotls o f

i o l

Zittauor iiiucliirio

pig. I-Arriingciiieiit. nT rollerB and niethods of tiireuding-up the clot Ii iii vurioiir tplirn ( ~ 1 purlding iiiiiriglt:s

It. is also rocommontlocl that tho padding trough ~houl t l ho RY small as pirssilde (not more than 6 gull. capacity) to avcrid ~ i t ~ t n g n irf liquor, and this should be fitted with a closed steani c - o i l irr Htoani jackot and connoctcd to a foed tank fitted prefrriibly with a stirrer antl also with a c l o d staum roil. AII axpantlor should bo fittocl in front of the intinglo to prm-ont. creasing of tho materials to bo patldetl, antl t h o nitunglo should b n gearod to run a t speeds of 15-20 yd. por niin. and iipwnidn. Expcrimonts should a h be carripd out on vnriciiis types of clnth with differing mangle settingn in orilor to (letormine the degree of oxprossion of tho mangle us this is a very important. point. This is easily rhterniined by passing a known weight. of dry c,luth through the mangle containing wator ancl Calsolune Oil HS antl tlotormining tho weight of liquor absorbed. The padding mangle fihoiiltl be fitted with a batching roller worked liy a d i p bolt I)I' a "plaiting down" arrangoniont; batrhing against t h o rollers by frict ion with voi.tical man@ is not. rocoinnierido~l. It, i R also important tha t RII pttl'tfl of tho rIlallgh3 shoiiltl 1)O rORdily accossiblo and

Prctltlin~-'l'lio actual padding consists simply of passing t h o dry prepared goods through the liquor at such a spood and ternperaturo that, tho gauds are thoroughly wet.tecl out; with heavy materials of tho cluck cloth typo, it. may tre atlvisablo t o pad H ~ V O Y ~ I times. The level of tho liquor in ilie troiigh during padding is maintained by feeding froin the stock tank, antl a t the end of the padding operation the t.roiig11 ~hoiiltl he full. Tho tmnperaturo of the padding liqiior may vary from 60%. to just. below b.p., antl is de te rmind hy tlio type of goods boing padded, heavy goods boing putltled at high temperatures. Cure, however, should be taken to maintain the same tenipera- t w o throughout the padding operation.

I t ~hiiiihl h r t)oi.no i n rninil that, during paddinK, tho pressure of tho rollers should bc atljustetl to give a Irmxiiniiiil 1.xprixA)n o f liqiiiir, IIH too " ~ l ~ p p y " ~ ( J O ~ H

cnniiut be lc4't for any Icngth of timo without further procesaiirg, uro difiicrilt to dry (if this is found necessary), and rapidly wneli "down" during the reduction procesn.

t.asily cl1~llnetl.

Af'tnr pii~ltling, tlio goo(ls aro oither lmt(.hcd up I)ohincl tho mringlo or plait c ~ l (lowti i i i i t l t w o t l i tw cithor tlrirtl or r u n on t o jigs i n tho w r t . nttito for rntliic,ing ~ n t l tlycting. 'l'hn goods (tun t)o loft for sovornl h o i i r s l)rfurc* c i r tift(*r drying nncl Irnfort5 rotluction, hiit, ninst t int htq l c f t in tiny

conio in conttict with thom, othorwiso tho patl(led colour will be locally wanhotl out .

It, is not I I ~ C P ~ H ~ ~ S . to dry pndtlings Imfore rotlnction. hut , , in gotioral, lintrn tlyors prefer to carry out this proceas. and in doing 80, cnro must bo tnkon t c r dry the g( io( l~ ~ l ~ w l y in ortlor t~ prt.vc*nt "Riding" 0 1 thc. v o l o u r which CHIIHOX sputt,otl effects, o r drying through uf the ilya u.lii(.Ii will C ~ I I H B a two-sitlrd effect. I t is atlvisablo to lap the first. fow cans with Calico when using drying cylinders and rcduro the stcam pressure to a mininiiini. The goods, either wot or dry, are then divided up into niiitable lengthrc for rectuct.ion on tho jig, end fents Htit(8hetl on, using fiat Rewings, and are batchctl up on tho jig in tho normal mannor, taking care that the paddings are not rubbed or wetted locally in nny way. The reduction ba th is then proparod, using thc quantities of reducing agents norinally used for the tlyea eniployetl, antl reduction nnd dyeing carried ou t during 4 to 6 ends at a tcinpernture which ia determined by the propcrties of the dyes being usctl. It, will also usually be found necessary to make further additions of dye to tho bath fur rrhatling and atrerigthcninfi purposofl; t,his should bc taken froin the liquor rcrnaining in the padding bath, which is reduced separately in a bucket, and added in 2 separato portions after the first and second ends.

Thero is always n tendency for dye to wash off f r o i n the pieces during tho first and second ends, the ainonnt deponding on the solubility and amount of clyo i w t l for the padtlings. Thcreforo, it is advisablo to allow tho h t h to s tand for u few minutes after the first and secoiicl ends in ortlor to allow this dye t o dissolv'r. I n i t in tho meantimcr tho batch niust. bo kvpt, awinging. Ilyring, hhncling. oxidation and aftcrr-t,rontriirrit tire (arr.ic(l o u t i n tho iiornmal manner. the arnountn o f rrdricing agents unil tho ttwiperii- turc tlttponding on the particular tlyo UHCCI.

&lethod of Cnlculating the Strength of the Padding L,iquw- The method of calculating the strength and amount, of tlio padding liquor to produce R tlcmirc?d shatlo on a given amount of niatorial in simple ancl dopeiitl~ 011 tho following

( I ) Strength of shatlc; ( 2 ) weight uf ninterinl; (3) exprossion of the padding mangle; and (4) capwity of tho padding box.

'rho amount of dye rtqnii.trd to pro(liico i i givoii shiitlt) is fiiwt tlot.nrn~inod by w t n n l Inbortitory ttwt,s or, if a shiitlc~ is lming patltlotl wliicli wtia previounly jig-(lyo(l, tho (Iyor will know t.ho arnount~ of ci)lonr roqiiircvl for i i givon timounl of inat orial. It, tnust, t)i) notncl, howcrvor, thu t tho tlytv ~tioi11d tilwtiys t i i i n t o nntlor-pn(l. sinco whcrn tho shtido dycw up on tho light n i i l n on tho j i K , i t i H a sirtiplo nint.tm t o ntltl iiioro ixrl(.riir, but, on t l i o ottior hnntl, if too tlecp t i shado i H obtainc~tl on pu(lding. i t is no('wrctiry 1 1 1 wnsli tho coloiir off prior to r ( ~ I i i e t i ~ i n o i i tho jig. r w l r y un(l rt'-(wnnionco pti(l(ling wit 11 u t'nrthor c i t l just c ~ l 11tu111 IIIK liiluor. 'l'lior(~foro. i t . i H rilwtiys rc.c.riiiirnc\nll(,(l t h t i t r i sll iul l piwe i r f tlirr r ivt i iul c , l o t h Iwing ptidtlvd ~ h o i i l ~ l I)o itistrrtcvl i n tlio firat ond f b i i t c i l ' tlio g(i(r(1a tincl pcidckvl throiigh tho i i ( . t i i t t I ninnglo, rind t l i r n r ~ ~ l i i c ~ c d tincl uxiclis;td in o r ~ l c ~ ~ . to Kivu nn indiciit~ion of' t l i e atrongtli r i n d H l i t u l o of tho paddiiig to ontildo any udj i ia trnc i l t s t o t x t made to tho padtlinC: liqnor. A sinilrlcr ~ i i c t l ~ o ~ l . I i~)wc~vvr, is I o r . r ~ ~ . t ti H l l l i i l l nitinglo tiIongsi(Ic tlio n(:Iii~iI ~ i i r i n ~ l ~ ~ , l i i i c l t i ~ l j u s t

sniull incinglc cun thon lw usotl for tests on f i l n t i l l p i o w n 0 1 i l i e actntil c I i ) t l i t c r lro 1rri(l i lvfl witli Iiqii~ir t t i lcon froni 1110 pu(lding box of t.ho Iiirgo ~~iai igl i i .

WIHII tho ciilwunt c J I ' tho (lyo roquirocl lius h r o n m(w- tainod, tho volutne of l i (por to be iiiudo up is crilciiltitod from the equatioii-

of tho (IyOhOllHO W1iHI.O llr0l)H of \Vtltt!l. Lrt! likoly 1 , I r

fact OrH-

tho C+XI)IY'HHiOIl Of thf) 1.01101.Y t 0 t h o HUI I I ( ' l1OgN!O. ' L ( l I IH

r = - 100 x 10 + c'*

where -4 = weight of (+loth; B = exprcssion of padding ivllera; (' = capacity of pntlding box in gall.; tind x = volume of liquor in gall. Thus, in ortler to pat1 1,000 Ib. cloth t o I I 2000,& ahado with a Calcdon Jade Urcon XS

Drc. lo l l HOPKINS-“PIGMENT PADDING PROCESSES O F APPLYING VAT DYES” 361

Paste Fine dispersion using Go gall. Calsolene Oil

HS, the expression of tho rollers being 80% and the capacity of the padding box 5 gall., the total volume of liquor required would be-

8y0t :’:: + 5 = 85 gall., which would contain-

86 20 = 2001b. dye and - = 0.85 gall. Calsolene 100 100

l’ooo

Oil HS. As is usual with all pndding operations, t.he first padding

to a shade is the most difficult, since it will be found that for the production of most shades, particularly mixtures, various adjustments of the padding liquor as regards concentration and component dyes will be necessary to give a reasonable match t,o a pattern on subsequent reduction, oxidation, etc. However. as the dyer becomes more efficient in the use of the padding mangle, he will find the syst,em to be easier and more reliable for the production of consist.ent results. It should be emphasisetl that once the chief fact,ors have been determined for producing a shade, no difficulty should be experienced in obtaining reanonablo repeats with similar materials. I t cannot be expect,ed that exact niatchings to any pattern will be obtained by padding, but results should be obtained which will permit of normal shading on the jig with reasonably small amounts of dyes. Generally, the results are quite satisfactory if padding yields an BFi-95% depth of shade of the pattern to be matched, the remainder of the dye required being added as shading over the first 2 en& during reduction on the jig.

There is no limit to the number of pieces which can be padded in one run to a particular shade and, even with long runs of cloth, there is no necessity to adjust the strengt,h of the feed liquor since the strength remains constant as the fibres h+ve no affinity for the pigment dye. In the case of long runs of cloth, however, the pigmenting liquor always shows a alight tendency to weaken, and t,his should be counteracted by thickening the padding liquor with a lit,tle gum tragacanth, e.g. &-$ gall. of a 1 : 20 gum-water paste per 10 gall. padding liquor. The use of thickened padding liquor also has the advantage that more even dyeings are obtained on cotton-viscose rayon union goods. In such cases it is preferable to dry tbe goods after padding, the gum preventing the transference of pigment in the subsequent reduction bath and conse- quent heavier dyeing of the viscose rayon. The amount of thickening added in all cases should be kept to a minimum, since it retards the wetting-out action of the padding oil, thus necessitating a slower padding speed and a higher temperature of the liquor.

The pigment padding process may be varied by omitting the padding oil from the padding bath, and adding it instead to t,he last wet pretreatmen$ of the materials prior to padding, and drying it in. In this case, the strength of the solution containing the padding oil should be adjusted so that the amount of the oil contained in the dried cloths is 1 Ib. approx. of oil per 100 Ib. material. The results given by this process are very sitliilar to those obtained bythealternative method,and as far as the present author is aware, the process offers no advantage, particu- larly when relatively small batches of material are being processed. It is used largely, however, by American dyers.

Many attempts have been made to perfect a method of production whereby materials may be padded with a vat dye, followed by reduction, oxidation and soaping in one continuous operation, but it is not a practical proposition since the pigment dye is partially washed off during reduction before being redyed on to the materials and, therefore, there would be a continuous change in the composition of the reducing bath leading to the production of unlevel dyeings.

Pigment Dyeing of Loose Cotton and Viscose Rayon “FibTo” in Open Vessels-It is possible by the foregoing method to produce very even dyeings t,hroughout the mass of loose materials, and the method is particularly recommended for dyeing light shades with mixtures which are normally difficult to dye level. The amounts of dyes used are exactly the same as for the ordinary method of dyeing, but only Paste Fine, 200 or 300 Grains or 300 Powder

Fine brands should bo used. Tho necessary amounts of dye are pasted well wi1.h a little hot wat,er and Calsolene Oil HS and then added to the dyebath, which should contain as small an amount of soft boiling water as will enable the loose materials to be worked easily. The dry loose cotton or “Fibro” is then entered into this bath, which contains 2 Ib. Calsolene Oil HS por 100 gall. water, and the whole is gently boiled for 10-15 min., meantime working the material well. The steam is then shut off and sufficient cold water added to bring the temperat,ure down to the normal dyeing temperature of the dyes used. The requisite amounts of caustic soda and sodium hydro- sulphite powder, depending on the dyes used, are then added, the colour allowed to vat for 10 min., and the material worked for a further hour in this vat until dyoing is complete. After hydroextracting, the dyeings are oxidised, washed, and soaped a t b.p. in the normal manner.

Pigment Padding of Cotton, Linen, and Viscose Rayon in the Hank, or Open Beck-This process is particularly recommended for dyeing pale level shados when penetra- tion is essential. The pigmenting process is best carried out on an impregnat,ing machine, the dry yarn being given several turns in the padding liquor and then evonly squeezed before the reducing and dyeing operations; but if such a machine is not available, a small tub capable of holding all the padding liquor can be used. As is usual with padding processes, previously prepared dry yarn only is used and, as yarn which is wet,ted-out and wrung well contains approximately its own weight. of liquor, it is necessary to prepare a volume of liquor equal in weight to 1% times the weight of the yarn to be dyed.

The same amounts of dyes are required as would be used for a dyeing carried out by the normal beck method, but Paste Fine, 300 Powder Fine, 200 or 300 Graim should be used. The dye is pasted with a lit,tle hot water, strained and then diluted t,o requisite padding volume wit,h water a t 6O0-9O0c. containing 5-10 lb. Calsolene Oil HS per 100 gall. The dry yarn is thoroughly impregnated with this liquor and efficiently squeezed, ensuring that none of the expressed liquor is lost, until all the yarn has been padded. The vatting liquor is prepared next, using quant,ities of reducing agents depending on the dye used, but retaining a little of the caustic soda and sodium hydrosulphite for vatt,ing the padding liquor which has not been used up. This liquor is diluted with cold water to the correct vatting temperataure, reduction carried out for 5 to 10 min., and the liquor added to the dyebath. The padded yarn is entered into the reducing liquor and turned well until exhaustion occurs. When the yarn is first entered, it should be turned as rapidly as possible, since a certain amount of pigmented colour dissolves in the bath and is washed off rapidly, but this is gradually transferred again to the yarn; for this reason, therefore, it is necessary to work the yarn vigorously to avoid any uneven transference of t.he vatted colour.

When dyeing is completed, t,he dyeing is oxidised, washed and soaped in the ordinary manner as used for yarn dyeing in open becks.

Dyeing Cops, Cheeses, Bearna, Hanka and Warps, and Loose Ooods in Open arul Closed Circulating Machines- The pigment padding of yarns in circulat,ing machines is the most recent development in vat dyeing, and has only been made possible by the introduction of vat dyes which yield such fine aqueous dispersions thnt there is no filtration of dye particles from the pigment,ing liquor on circulation through tight>ly packed or wound yarns. This process is only to be recornmended for producing pale shades with dyes which have such a high affinity m to cause uneven dyeing even though iised in conjunction with retarding agents, and only the Cttledon Paste Fine brands arid 200 Grains are to be recommended for use. The technique for dyeing yarns in warps or bundles and loose goods varies slightly from the method of dyeing cheeses, cops, bobbins, etc., since in the former case, packing the machines is done by hand and is liable, therefore, t,o variation, whereas in the second case, the winding is mechanical and consistent. However, with warps and bundles and loose goods, particular care should be taken to pack the machine so that no channelling of the liquor can possibly take place and yet the pack is 80 arranged that all the material will be uniformly

362 HOPKINS-“PIGMENT PADDING PROCESSES O F APPLYING VAT DYEE” Dec. 1941

impregnated. This is a most important point, since if the yarn is not evenly saturated with liquor, uneven dyeing will occur.

In the act.ua1 pigmenting operation, the highest, concen- tration of padding liquor permitting satisfactory *orking of the machine should be used; it is prepared by stirring the dyes into a thin paste with hot water and diluting to padding volume, filtering and t.hen adding Calsolene Oil €IS in tbe proportion of r-10 lb. per 100 gall. liquor. The padding temperature may vary from t30°-1000c., but must be maintained a t a constant t,emperature during padding. This liquor is circulated through the dry materials for 16-20 min., but after the goods have been thoroughly impregnated. i.e. in about 6 min., the circulation should be stopped and preasureon the goods adjusted to give a more even packing. When pigmenting is complete, the liquor is pumped into the storage tank and diluted with cold water until the correct vatting and dyeing temperature is reached and, if possible, excess liquor in the goods should be extracted by vacuum or hydro- extraction and added to this liquor. The correct amounts of caustic soda and sodium hydrosu1phit.e depending on the dyes used are added next, t,he vat allowed to stand for 5-10 min., the machine then restarted and dyeing carried out for a further 40-60 min. After hydroextract,ion, the dyeings are washed with cold water, oxidised, and soaped at b.p.

When this method is employed, exhaustion of the dyeing liquor is fairly rapid, but even when complete the machine should be run for a further 20 min. at least to ensure levelness of the dyeing.

The processes of pigment dyeing with vat coloura as described are those in use now in the trade in this and other countries, but, so far, comparatively little pig- menting of yarns has been carried out, although this practice was rapidly growing prior to the beginning of the present war.

Thanks are given to I.C.I. (Dyestuffs) Ltd. for permission to give this paper.

DISCUSSION Mr. C. D. Smith said that the calculations involved in

determining the amount of dye, etc., were not clear to him. Would the Lecturer explain the system more fully?

The Lecturer said that a simple example would probably clear up any difficulty. Thus, in order to pad 100 lb. material in a 6% shade with Caledon Blue RCS Paste Fine, 5 lb. dye would be needed. If the mangle expression was rated at SOY0, 8 gall. liquor would be absorbed by the dry material so that there should be 6 lb. dye in 8 gall. liquor. If the capacity of the padding trough was 4 gall., the total quantity of liquor required would be 8 + 4 = 12 gall. containing 7.5 lb. dye and 1% Calsolene Oil HS, assuming that the dyer did not want to use all the padding liquor, a s 4 gall. liquor containing 2.6 lb. dye would be left in the trough which should be full or nearly full on com- pletion of padding.

Mr. R. A. Peel said that in his experience of dyeing cotton and rayon furnishing and casement fabrics-with vat dyes he had used both tho pigment padding process and the usual vat dyeing process on the jig. Although the Lecturer had referred to the difficulty of obtaining consistent shades by the latter method, he had not men- tioned the relative cost of the two processes. I n his (Mr. Peel’s) opinion the excessive cost of the pigment padding process outweighed its other advantages in dyeing piece goods of the types mentioned, and shade matching was not any easier in the pigment padding process than in ordinary jig dyeing. In preparing cotton or cotton- rayon piece goods, did the Lecturer advocate a caustic alkali boil, followed by hydrochloric acid souring, or the soda ash boil? Was it necessary to remove all starch where starch size was present? Also, why did the Lecturer condemn friction padding? He (Mr. Peel) had found that the common friction pad, i.e. 2 cotton-covered iron rollers, admirable for pigment padding heavy slub cloths of viscose rayon warp and 2-fold cotton weft. Did the Lecturer consider that pigment padded vat dyeings were less likely to cause tendering than jig-dyed vat dyeings, particularly in brown, gold and fawn shades?

The Lecturer said that pigment padding was a more expensive process than vat dyeing, since more dye is required owing to the higher degree of penetration obtained, and there was also the addit,ional cost of padding

oil. The differences in cost were most apparent when short runs of cloth were being dyed, since more labour was necessary in set.ting up the padding manglo to each recipe and cleaning after padding. The amount of labour involved was much less, of course, when long runs of cloth were being padded. The advantages gained by pigment padding were apparent both in levelness of shade and penetration. These properties were determined by the type of goods being processed, as it was obvious that little improvement would be shown on a loosely woven material compared with a heavy duck cloth, so that t,he use of the process in any particular case was a matter for the discretion of the dyer. The pigment padding process was used largoly on the materials already mentioned, as it overcame the defect known as “pulled effect”, which showed up undyed white spots on ordinary jig-dyed materials when the warp and weft were disturbed.

The mode of pretreat,ment of the goods to be padded was again determined by their construction, light goods being usually boiled out in soda ash, whereas heavier materials, particularly drills and duck clothe, were boiled in caustic alkali. Goods containing viscose or cellulose acetate rayon should not be boiled, but scoured in hot soap and ammonia. It was not necessary to desizo cloths before padding, but bet,ter results as rogards penetration were obtained on desixed materials owing to their higher degree of absorbency. Friction padding was not condemned, but it was not advocated for light goods, particularly if lapped rollers were being used, owing to risk of per- manently damaging the material. The best results were given by using a mangle with a fairly soft and flexible nip. Friction batching, however, was not good practice owing to the possibility of producing rub marks on the padded goods. The pigment padding process had no influence in modifying the tendering properties of certain vat dyes so that, wherever possible, non-tendering dyes should be used.

Mr. R. Greenlees asked if the method of application described by the Lecturer could be employed in dyeing azoic colours?

The Lecturer said that he did not know any successful practical method of applying azoic dyes by the pigment padding process, although this met,hod had been investigated.

Mr. J. Bruce said that, in the pigment padding method, it seemcd to be necessary to assume that an almost perfect padding mangle would be used, just as was the case in padding any ot,hhar insoluble material on cloth. Could some latitude be allowed in padding vat pigments, and did the subsequent reduction on the jig even up any uneven dispersion of pigment?

The Lecturer said that, in general, a padding mangle need not be perfect to give sat,isfactory results, particularly if medium and heavy shades were being dyed, as small faults were covered up during the subsequent jig-“dyeing” operation. I n padding light shades on mercerised poplins, however, t,here was not sufficient, dye used to cover up any unequalities caused by padding and, therefore, in such cases the expression of the mangle should be con- sistent throughout its width.

Mr. T. J. Brown asked if it was possible to pad the vat dye and subsequently reduce and dye on the winch, particularly in t,he case of certain types of clothe which were not suitable for jig treatment?

The Lecturer replied in the affirmative. He said, however, that when reducing on the winch, excessive washing off of pigment occurred before reduction was complete, and to overcome this defect, it was necessary to add salt to the reducing bath. A still better method was slightly to thicken t’he padding liquor with gum and dry the cloth carefully before the reducing operation, whereby very little loss of pigment dye occurred in the reducing bath. Moreover, shades having excellent solidity on unions were obtained by this method.

Erratum In the last line of the left-hand column (this Jouc.,

1941, 57, 327) f o r 30%. r e a d 304”c.